Viscosity compensated turbine flow meter



Dec. 5, 1967 H. KARLBY ET Al.

VISCOSITY COMPENSATED TURBINE FLOW METER '7 Sheets-Sheet 1 Original Filed Feb. 2 1959 H. KARLBY ET AL VISCOSITY COMPENSATED TURBINE FLOW METER Dec. 5, 1967 7 Sheets-Sheet Original Filed Feb. 2', 1953 VISCOSITY COMPENSATED TURBINE FLOW METER '7 Sheets-Sheet Original Filed Feb. 2", 1953 Wm M EE 95 miSw 9 5 302 9:33; H Km r we 956 33 35 3mm I ammo w3m -mwwH 5M INVENTORS //[/V/W/V6 finer M/m aro/v [Z155 Dec. 5, 1967 H. KARLBY ET AL 3,355,947

VISCO ITY COMPENSATED TURBINE FLOW METER Original Filed Feb. 2", 1953 '7 Sheets-Sheet 5 1N VENTORS %/e/v/v//v a 5mm BY W EYS

Dec. 5, 1967 H KARLBY ET AL 3,355,947

VISCO I Y COMPENSATED TURBINE FLOW METER Original Filed Feb. 26, 1953 7 Sheets-Sheet 7 ew M:

INVENTOR5 HEM/W6 A ien 3r l Wmsro/v A [5 AT ORNEYfi United States Patent O 3,355,947 COMPENSATED TURBINE FLOW METER Henning Karlby and Winston F. Z. Lee, Pittsburgh, Pa,

assignors to Rockwell Manufacturing Company, Pittsburgh, Pa., a corporation of Pennsylvania Original application Feb. 26, 1959, Ser. No. 795,755, now Patent No. 3,248,945, dated May 3, 1966. Divided and this application Nov. 24, 1965, Ser. No. 559,343

13 Claims. (Cl. 73230) This is a division of application Ser. No. 795,755, filed Feb. 26, 1959 (now Patent No. 3,248,945) for Viscosity Compensated Turbine Flow Meter and a continuationin-part of our application Ser. No. 634,662, filed Jan. 17, 1957 (now Patent No. 3,163,041), our now abandoned application Ser. No. 717,863, filed Feb. 27, 1958, and our now abandoned application Ser. No. 717,922, filed Feb. 27, 1958.

The present invention relates to turbine meters and more particularly to improvements in such meters which render them substantially free of metering inaccuracies resulting from the viscosity eifect of fluids of high viscosity.

An example of a preferred form of turbine meter adapted for high metering accuracy of low viscosity fluids and having no viscosity compensation is disclosed in our now abandoned application Ser. No. 717,863, filed Feb. 27, 1958.

It has been established theoretically and experimentally that the meter disclosed in said application is satisfactory for high accuracy measurement of fluids of low viscosity such as air, gases, water, gasoline, fuel oils, etc, but that without proper modification, it does not meet extremely high accuracy requirements such as :L0.l% allowable deviation over a flow range (Q Q mm of 5) for high viscosity fluids such as crude oils of high viscosity ranges from a minimum of 35 SUS to a maximum of 5000 SUS as required commercially, particularly where fluids of diflerent viscosities must be metered by the same meter. The main trouble is due to the fact that in turbine meters of that type, the driving force is proportional to the square of flow (Q whereas the resisting force (F,) is proportional to an exponential power of flow (Q) less than the square in fluids of high viscosity, the exact magnitude of which depends upon the Reynolds number of the existing flow condition.

As is well known, the Reynolds number is a dimensionless expression which presents the characteristics of a fluid flow in terms of the velocity of the fluid, the dimensions of the element through which it flows, the density of the fluid, and the viscosity of the fluid. The Reynolds number is directly proportional to the velocity and density, and inversely proportional to the viscosity of the fluid.

In conventional practice, meter accuracy curves are plotted by graphically presenting the ratio of the turbine velocity to the rate of flow through the meter w/Q versus. the flow rate Q. Such a curve gives information about the meter accuracy when fluid of only one viscosity is metered. If fluid of another viscosity is to be metered, another accuracy curve is required to reflect the meter characteristics in fluid of the new viscosity.

After a great deal of study, it has been determined that a much more useful meter accuracy curve can be obtained by plotting the ratio of turbine speed to flow rate, w/ Q versus the Reynolds number of the flow through the meter taken at a significant point within the meter. It has further been determined that the Reynolds number of the flow through the turbine blades of the meter provides the best representation of flow characteristics through themeter. Thus, the blade Reynolds number VISCOSITY 3,355,947" Patented Dec. 5, 1967 is utilized as the base against which the ratio of turbine speed to flow rate w/Q is plotted to give an extremely useful accuracy curve for a meter.

One particular advantage of such an accuracy curve is that fluids of various viscosities, when passed through the meter at varying flow rates, all yield points which may be plotted on this curve. In effect, there is but a single accuracy curve for the meter as apposed to the system in which the flow rate is utilized as the base for the accuracy curves and in which system a separate and distinct accuracy curve must be plotted for each viscosity of fluid that will pass through the meter.

To further illustrate this concept of Reynolds number accuracy curve, it will be seen that it is quite possible for a fluid of relatively low viscosity, flowing with a relatively low velocity, to have the same characteristic of flowand Reynolds number-as a relatively viscous fluid flowing at a higher velocity. Further, each of these fluid flows will result in the same ratio of turbine speed to flow rate w/ Q so that they can be plotted as a single point in the Reynolds number accuracy curve. If, however, the two fluid flows were plotted as points on accuracy curves utilizing the flow rate as a base, they would be points on two separate curves, each of which would be peculiar to only fluid of the same viscosity as that utilized in the test.

In a conventional system of plotting the ratio of w/Q versus rate of flow Q, the plot must be a horizontal straight line in order for the meter to accurately meter fluid of a given viscosity at all rates of flow. If fluid of another viscosity is to be metered, another accuracy curve must be plotted and this, too, must be a horizontal straight line if the meter is to accurately meter fluid of that viscosity. When utilizing a meter accuracy curve which depicts the ratio of turbine velocity to flow rate w/ Q versus the blade Reynolds number, only a single meter accuracy curve need be considered for fluids of all viscosities. If this accuracy curve is a horizontal straight line, the meter will accurately meter fluid of any viscosity at any flow rate.

Physically, no meter has yet been constructed which will accurately meter fluid over the entire range of Reynolds numbers. For all practical purposes, however, a range of Reynolds numbers for a specified metering purpose may be selected. Thus, considering the maximum and minimum flow rates and the maximum and minimum fluid viscosities desired for a particular application, a range of Reynolds numbers may be selected which will include all possible combinations of viscosity and flow velocities within the desired limits. A meter which has a horizontal straight line for a blade Reynolds number accuracy curve over the selected range of Reynolds numbers will, accordingly, meet the specified metering requirements.

Experimental results indicate the turbine meter disclosed in our copending application Ser. No. 717,863 has a straight line blade Reynolds number accuracy curve over the high Reynolds number range. However, at the lower Reynolds numbers which are a result of high viscositiesthe accuracy curve of the meter does not remain a horizontal straight line. Instead, the Reynolds number accuracy curve of a turbine meter of that type will have a hump in fluids of high viscosity for flows within the operating range rather than a flat curve: as in fluid of low viscosity. It is therefore necessary to introduce some special device into a turbine meter of that type to eliminate the viscosity effect of fluid of high viscosity on the meter accuracy.

The present invention therefore contemplates the provision of a special turbine meter for accurately metering and recording the flow of viscous and extremely viscous fluids and comprises a metering turbine disposed in a conduit in the path of fluid flowing through the conduit and means for substantially eliminating the viscosity effect of the fluid as it passes through the metering turbine.

With the foregoing considerations and purposes in mind, it is the major object of this invention to provide means for changing the natural Reynolds number accuracy curve of the meter disclosed in our copending application Ser. No. 717,863 so that the resulting changes will flatten the accuracy curve in the range of lower Reynolds numbers and allow fluids of higher viscosity to be accurately metered.

It is further the object of this invention to provide an improved axial flow turbine for substantially eliminating variations between the absolute meter inlet fluid velocity and the absolute discharge fluid velocity engendered by the viscous drag of the fluid being metered.

It is further the object of this invention to provide an improved axial flow turbine embodying a rotatable metering turbine and means for compensating for the slip of the turbine due to the viscous drag of the fluid, thereby maintaining a linear relationship between the angular speed of the turbine and the volume rate of the fluid passing through the turbine.

It is further the object of the present invention to provide an improved axial flow turbine meter embodying a free counter-rotating turbine with a controlled viscous drag device disposed coaxially with and at a proper distance upstream of the register driving metering turbine, the effect of which is to create an additional driving force of the meter turbine and to substantially eliminate metering registration inaccuracies attributable to the viscosity of the fluid being metered.

More specifically, it is an object of this invention to provide an axial flow turbine meter embodying a free counter-rotating turbine having an additional viscous drag surface, the magnitude of which is adjustable and which is disposed coaxial with and at a proper distance upstream of the meter turbine and in which the blade angle of the blades of the free turbine is so correlated to the blade angle of the blades of the meter turbine that the absolute exit velocity of fluid from the metering turbine is substantially free of any tangential component regardless of the different viscosities of different fluids.

A further specific object of this invention is to provide an axial flow turbine meter embodying a free counterrotating turbine disposed coaxial with and at a proper distance upstream of the meter turbine and having a viscous drag cup mounted for rotation with the counterrotating turbine for inflicting a viscous drag force, the magnitude of which is adjustable and is a function of the viscosity of the metered fluid so that the free turbine is effective to impart a tangential component to the absolute exit velocity of fluid passing therethrough which is substantially equal and opposite to the change in the tangential component of the velocity of the fluid as it passes through the meter turbine.

These and other objects of the present invention will become more fully apparent as the description proceeds in connection with the appended claims and the annexed drawings wherein:

FIGURE 1 is a longitudinal sectional view of a turbine meter illustrating one embodiment of the present invention;

FIGURE 2 is a longitudinal sectional view of a turbine meter illustrating a further embodiment of the present invention;

FIGURE 3 is a plot illustrating the relation between total turbine slip (S due to fluid friction and the blade Reynolds number of the fluid flow;

FIGURE 4 is a plot illustrating the blade Reynolds number accuracy curve or the relation between the angular velocity of the metering turbine per unit volume of fluid flow and the blade Reynolds number of the fluid flow;

FIGURE 5 is a longitudinal sectional view of a turbine meter illustrating another embodiment of the present invention in which the metering turbine is equipped with a controlled viscous drag device in the form of a viscous drag drum;

FIGURE 6 is a plot illustrating the improvement of the blade Reynolds number accuracy curve of a turbine meter due to the controlled viscous drag device provided on the metering turbine;

FIGURE 7 is a longitudinal sectional view of a turbine meter illustrating a further embodiment of the present invention equipped with a free counter-rotating turbine with a controlled drag device in the form of a viscous drag p;

FIGURE 8 is a diagram illustrating the synchronous speed condition of the meter of FIGURE 7; and

FIGURE 9 is a vectorial diagram illustrating velocities at synchronous speed for a meter which does not compensate for fluid viscosity.

This disclosure of the present invention will proceed with an anlysis of the operation of turbine meters and the relation thereof to the embodiments of the present invention followed by a detailed description of the constructions embodying the principles of the present invention which includes a detailed explanation of the significance of each of the several aspects of the present invention.

FIGURES 1, 2, 5, and 7 illustrate turbine meters constituting practical embodiments of the principles of the present invention for use in metering fluids of various viscosity. Referring now to FIGURE 9, velocity vector diagrams are illustrated for the synchronous speed condition of a turbine meter without viscosity compensation as illustrated in FIGURE 19 of the above-identified copending application (Ser. No. 717,863) and hereinafter referred to as the Type I turbine meter.

With continued reference to FIGURE 9, the velocity v is the absolute velocity of the fluid at the inlet to the metering element or the metering turbine, velocity v is the absolute discharge velocity of the fluid from the metering element and velocity rw is the linear velocity at a radius r of the metering element rotating with an angular velocity w. Velocity v is the discharge velocity of the fluid relative to the rotating metering turbine. For a particle of fluid moving along the blade with a velocity v relative to the blade, the particle will leave the blade at A with the velocity v if the blade is at rest. If the blade is moving in direction shown with a magnitude rm, and the velocity of the particle still has a velocity v relative to the blade, and remains in contact with the blade to the end A, the absolute velocity of the fluid as it leaves the blade at A will be the vector sum of the velocities v and rw. Thus, the vectorial sum of the turbine velocity and the relative velocity will yield the absolute discharge velocity v In a theoretically perfect system where no resisting torques are encountered in passage of the fluid through the metering element, the absolute discharge velocity would be vectorially equal to the absolute inlet velocity of the fluid being metered sincethere would be no slip of the turbine. Hence, all of thefluid passing between the blades of the turbine would be metered and recorded and the value of the ratio w/Q' would be the ideal value indicated by the horizontal straight line in FIGURE 4. Under actual conditions, however, there are resisting forces, as will be described, of such nature and magnitude to cause significant turbine slip and thereby affect the accuracy of the meter unless compensated for. As used in this application, slip will broadly designate those effects which tend to bring the actual value of the ratio of turbine speed to flow rate w/ Q below the ideal value that would result if all the fluid passing through the turbine were metered and recorded. This turbine slip due to prevailing forces resisting the rotation of the turbine is evinced by and directly related to the tangential velocity component v of the fluid flowing through the turbine. Such a tangential velocity vectorially adds to the absolute inlet velocity v to give the resultant absolute discharge velocity v As the viscosity of the fluid changes, the resisting force is changed for a given flow rate, resulting in a corresponding change in the tangential velocity v especially'in the region of the lower Reynolds numbers. This change of the tangential velocity v results in turn in a varying turbine slip which is effective to adversely affect the accuracy of metering registration.

The following analysis serves to exemplify the effect that the resisting forces resulting from fluid friction and mechanical friction have on the accuracy of a turbine meter.

Analysis of the turbine meter in fluids high viscosities By means of flow straighteners and proper design of the turbine housing and approaching hub, the inlet velocity v to the blades of the turbine can be assumed to be purely axial and uniformly distributed across the entire annular flow passage leading to the metering turbine.

Consider first the turbine meter of FIGURE 1 being steadily rotated in synchronous condition by a fluid of high viscosity and having the velocity diagrams shown in FIGURE 9. Since the driving force P exerted upon the turbine by the fluid can be no greater than the resisting force F of the turbine, it will be useful to analyze the resisting forces on the turbine and to consider their nature.

It can easily be shown by basic laws of fluid dynamics that the driving force F exerted on the turbine is equal to the mass rate of flow m through to the meter multiplied by the change in absolute tangential velocity v of the fluid passing through the meter or F =mv The mass rate of flow m is equal to the density of the fluid p multiplied by the volumetric rate of flow Q or m= Q.

Now, if the turbine were in the ideal state, having no resisting forces of any kind, the turbine would move in exact timed relation to the fluid flow and no force would be required to drive it or F would be zero. This is readily apparent since the fluid would not be deviated in a tangential direction as it passed through the turbine so that v would equal v (FIGURE 9) and v would equal zero.

It is unnecessary to note that this ideal condition cannot exist and that the turbine has resisting forces which must be overcome by the force created by the fluid flowing through the meter. In a meter turbine, as opposed to a power turbine, the forces F to be overcome by the driving force R; are relatively small. They may be conveniently considered to be of two classes. The first is a resistance force F due to the mechanical resistance of the friction created by the bearing loads and the register load. Because of the construction of the turbine meter with magnetic shaft suspension, magnetic register drive and low-torque register, as fully discussed in our now abandoned application Ser. No. 717,863, the mechanical resistance force F is held to a minimum. Further, it is relatively constant and independent of the flow rate Q. For these reasons, the mechanical resisting forces F have no appreciable effect on the accuracy of the turbine meter in its operating flow range and may be disregarded for the purposes of this analysis.

The second resisting force which must be considered is the force due to the fluid friction acting upon the rotating parts of the meter. While the fluid exerts a resisting force on the spokes of the turbine, the hub of the turbine, and all other rotating parts, it has been found that the greatest resistance force acts upon the blades of the turbine. By proper design of the turbine, it is possible to minimize the fluid resisting force acting upon the parts of the turbine other than the blades so that it is only a very small fraction of the resisting force acting upon the turbine blades. For the purposes of this discussion, the resisting force acting upon all parts of the turbine except the blades may be considered to be negligible. The resisting force F created by the fluid friction acting upon the blades of the turbine should be considered in some detail to gain an understanding of the present invention.

However, before considering the fluid friction resisting force F acting upon the turbine blades, some attention will be given to the characteristics of flow through the turbine meter. Considering for the moment a fluid of fixed viscosity and density flowing through the meter, at very low fl-uid velocities, the flow through the meter is laminar. As the fluid velocity increases, areas of turbulence develop until finally, the flow of fluid through the meter becomes completely turbulent.

Just when this change of flow characteristic takes place depends upon the nature of the fluid flow passage. For any turbine meter, there is fluid velocity for any particular fluid below which turbulent flow cannot take place and all flow is laminar. Since this flow rate .is for a particular fluid (i.e., a fixed density and viscosity) and through a particular flow passage (i.e., the blade area of the turbine meter), it may be expressed in terms of the Reynolds number. Thus, the Reynolds number below which only laminar flow takes place is designated as the critical Reynolds number and is so indicated on FIGURE 3.

The high Reynolds numbers indicate the range Where the flow is completely turbulent. The change of the flow characteristics from a laminar flow to completely turbulent fiow is not an instantaneous occurrence at the critical Reynolds number, Rather, because of the nature of flowing fluid, there is a transition zone embracing those Reynolds numbers immediately to the right (FIGURE 3) of the critical Reynolds number in which the flow is partially turbulent and partially laminar. This area creates difliculties in predicting exactly how the turbine will behave. However, since the present invention teaches the use of a single blade Reynolds number accuracy curve to show the characteristics of the meter, it is possibleby utilizing this accuracy curve-to analyze the effects of the flow in the complete range of Reynolds numbers and to compensate for them in a manner to be described.

Returning now to the resisting force F; acting upon the blades as a result of the fluid friction, it is this force which creates the major deviations from the ideal in the blade Reynolds number accuracy curve. To indicate just how these forces affect the turbine operation, the fluid resisting force F for each of the three ranges of flow patternslaminar flow, turbulent flow and transition zone are analyzed and their nature determined.

In the laminar flow range, the fluid friction resisting force created by the fluid passing over the turbine blades is of a viscous nature and will be designated F This resisting force F acts parallel to the blade surface and so has a tangential component which is opposed to the turbine driving force F This resisting force F, is the predominant cause of the change of tangential velocity v through the turbine in the laminar flow range. To determine the nature of the resisting force F due to viscosity, reference may be had to the basic force equation Here, the driving force F required to overcome the viscosity resisting force F is equal to the density p times ,the volumetric rate of flow Q times the change in tangential velocity due to the viscous friction of the fluid v Since the resisting force F due to the viscosity effect is proportional to the viscosity ,u of the fl-uid times the volumetric rate of flow Q, it may conveniently be expressed as where K=a proportionality constant. The term K hereinafter will be utilized indiscriminately to designate any undefined proportionality constant without subscripts or modifications except that K will be utilized when two diflerent constants appear in the same equation. Two different constants in the same equation will be designated as K and K.

Since the driving force F required to overcome the resisting force F, due to viscous friction must be equal to the resisting force F in the synchronous condition, the last preceding equations may be equated to each other so that Solving for the change in velocity due to the viscosity effect V it will be seen that Thus, tangential velocity change v due to the resisting force F of the viscosity effect is directly proportional to the fluid viscosity ,u. and inversely proportional to the fluid density p.

In the turbulent flow range, the fluid friction resisting force which acts upon the turbine blades is of a turbulent nature and will be designated F Here, too, the turbulent friction resisting force F acts along the surface of the turbine blades so that it has a tangential component which resists the rotary motion of the turbine.

As before, the driving force F required to overcome the turbulent resisting force F is equal to the density of the fluid p times the volumetric flow rate Q times the change in tangential velocity of the fluid through the turbine v or d"=PQ t2" Further, the resisting force F exerted on the turbine by the effect of turbulent flow is proportional to the density p times the square of the volumetric flow rate Q or At synchronous condition, the driving force is equal to the resisting force or Solving for the change of tangential velocity v due to the turbulent effect of the fluid,

t2"= Q Thus, the velocity change v "due to the resisting force F of the turbulent friction effect of the fluid upon the blades is directly proportional to the flow rate, Q and'is independent of the viscosity ,u of the fluid.

The resisting force F due to fluid friction in the transition zone results from various combinations of a turbulent friction resisting force F, and a laminar or viscous friction resisting force F.,. It has been determined that the frictional resisting force P of the fluid friction in the transition zone may be expressed bythe following equation:

F PQ K Q The expression KpQ is of the same nature as the turbulent resisting force F, and the-expression K Q is of the same nature as the viscous resisting force F As before, the driving force F required to overcome the fluid friction in the transition zone may be expressed by the basic force formula EdIIIZPQVtZIII Since the driving force F must equal the resisting force F in the synchronous condition, the last previous equations may be equated to each other. Thus,

and solving for the change in tangential velocity v due to the transition resisting force F tilt XQ- Having determined the tangential velocity changes in the fluid v v and v due to the fluid friction resisting forces F F and F, in the laminar flow range, the turbulent range and the transition zone respectively, it now will be determined how these tangential velocity changes affect the meter accuracy curve. In order to consider this situation, it must be remembered that the change in tangential velocity v directly evinces turbine slip. If no resisting forces acted upon the turbine, the tangential velocity change v would be zero and the ratio of turbine velocity to flow rate 00/ Q would be ideal, as shown in FIGURE 4. Since it is the ratio of turbine velocity to flow rate w/ Q which must be constant in order for the turbine to accurately meter fluid, it is necessary to see how the changes of tangential fluid velocity v affect this ratio. The amount that the turbine slips, or registers below the ideal value of'the ratio w/Q, will be directly proportional to the amount that the tangential velocity of the fluid v changes, divided by the flow rate Q. Thus, the slip of the turbine will be equal to Since v is a linear velocity tangent to the turbine, it must be divided by some radius r to correctly express the ratio of w/ Q. However, for a particular turbine, the radius r will be a constant so that the expression is an accurate expression of the slip S; in terms of the change of tangential velocity v of the fluid and the flow rate Q.

Referring now to the expressions for the changes of tangential velocities of the fluid in the laminar range, the turbulent range and the transition zone, it will be seen that the slip S; of the turbine in each of the ranges may be expressed merely by multiplying the expressions for the tangential velocity changes by the term K/ Q.

Thus, in the laminar flow range, the tangential velocity change v due to the viscosity resisting force F when multiplied by the term K/ Q yields the expression for the turbine slip Sf due to the viscosity force F or:

It will further be noted that the expression of S, makes it proportional to the fluid viscosity ,u. and inversely proportional to the fluid density p and the flow rate Q. This expression, then, is inversely proportional to the Reynolds number R. for the particular turbine meter or:

In the turbulent range, the change in the tangential velocity v due to the turbulent resisting force F when multiplied by the term K/Q yields the expression for the turbine slip S due to the turbulent force F, or

It will be noted that in the turbulent range, the slip S is constant, which does not impair the meter accuracy.

9 In the transition zone, the tangential velocity change v due to the fluid resisting force F when multiplied by the term K/ Q yields the expression for the turbine slip S;"' due to the resisting force F or K 1/! 5 v Q t2 wherein w ary-10E 10 Thus,

K'p. S "=K f PQ As has been previously stated in discussing the slip due to the viscosity resisting force F the expression K i/pQ is inversely proportional to the Reynolds number of the particular turbine meter involved or Referring now to FIGURE 3, it may be seen that the slip S; of the meter throughout the range of Reynolds numbers is plotted. In the laminar range, the slip S; varies in accordance with the expression 25 K S R is entered since the slip is due to the fluid resisting force F The blade Reynolds number accuracy curve of the Type I turbine meter is represented in FIGURE 4. As hereinbefore described, the ideal value of the ratio of turbine speed to volumetric flow rate w/Q would be a horizontal straight line over the entire range of Reynolds numbers, as indicated on FIGURE 4. However, the turbine resisting forces just discussed causes a slip S of the turbine which varies over the range of Reynolds numbers. This slip 8,, when substracted from the theoretical value of the ratio of 01/ Q yields the Reynolds number accuracy 55 curve. The accuracy curve for the Type I turbine meter, as shown in FIGURE 4, has been completely verified by experimental results. It has a hump around the critical Reynolds number before it reaches the flat part of the curve. For fluids of low and medium viscosities (such as air, natural gas, gasoline, water, thin oils, etc.) a Type I turbine meter of reasonable size (4 inch size and above) will mainly operate on the flat part of the accuracy curve for a reasonable flow range. However, in case of fluids of high viscosity, the accuracy curve will include the hump as well as the flat part, resulting in rather large maximum deviation. The critical Reynolds number of a turbine meter depends somewhat upon the initial turbulence of the flow before entering the turbine and the particular design of the meter. The higher the initial tur- 7O Extensive tests in a great variety of fluids (air, natural 7 10 gas, gasoline, Stoddard solvent, thin oil and thick oil) of the turbine meter disclosed in said now abandoned application Ser. No. 717,863 and several other models designed according to the above analytical findings show a good agreement between the experimental results and theoretical analysis.

FIGURES 1 and 2 illustrate one practical construction embodying the principles of the invention wherein a turbulence generating device in the form of a flow restriction, as will be described, is located a predetermined distance upstream from the turbine rotor to intentionally establish a large initial turbulence in the fluid flowing to the metering turbine. This large initial turbulence lowers the critical Reynolds number and thereby extends the turbulent range of the fluid so that a longer linear flow measurement range is available. The turbulence generated in the fluid stream further provides for a more uniform velocity distribution, particularly in the laminar flow range which also improves the meter accuracy of the meter for fluids flowing in this range.

With continued reference to FIGURES l and 2, the axial flow turbine meter therein shown comprises a cylindrical inlet conduit having a faired core section 22 supported coaxially therein by equiangularly spaced longitudinally extending ribs (not shown) and an outlet conduit section 26 having a faired core section 28 supported coaxially therein by spaced struts 29. The core section 22 journals a meter turbine 30 and contains a drive train to register within register housing 32, all of which, with the exception explained below, is of identical structure to the structure shown in our said now abandoned application Ser. No. 717,863, the disclosure of which is hereby adopted and incorporated herein by reference and thus requires no further detailed disclosure or explanation herein.

With continued reference to FIGURE 1, the exception referred to above resides in the provision of a flow restriction in the form of a sharp edged orifice plate having an inner frusto conical surface 42 beveled radially outwardly to define sharp circular edge 42a facing the flow of fluid. The orifice plate 40 is concentrically mounted in the tubular meter housing conduit 20 at the entrance to the annular channel 46 formed by the conduit 20 and core section 22 so that turbulence is created as the fluid passes into the orifice plate.

Referring now to FIG. 2, the surface illustrated therein for generating turbulence in the fluid stream comprises an annular plate 48 concentrically mounted on core sec tion 22 at the entrance to the annular channel 46. This orifice plate 48 has an outer frusto conical surface 43a beveled radially inwardly to define asharp turbulence producing edge 48b facing the flow of fluid.

The orifice plates 40 and 48 of FIGURES l and 2 respectively are spaced a suflicient predetermined distance upstream from the metering rotor 30 so that the initial turbulence established in the fluid does not impair the meter accuracy due, for example, to the eddy currents adjacent the discharge end of the orifice plates.

Consequently, it will be appreciated that the orifice plates 40 and 48 of the embodiments of FIGURES 1 and 2 respectively generate a large initial turbulence at a predetermined distance upstream from the turbine rotor 30. This increased turbulence lowers the critical Reynolds number as hereinbefore described so as to establish a greater linear flow measurement range. Thus, with reference to FIGURE 4, the hump 50 defined by the accuracy curve 52 at the critical Reynolds number is shifted back toward the ordinate axis to increase the range of the flat curve portion indicated at 54.

While the orifice plates 40 and 48 constitute the preferred generating device, the initial turbulence may also be generated or established by other devices such as a series of screens spaced a desirable distance upstream from the metering turbine.

While the establishment of initial turbulence will lower the critical Reynolds number of the turbine meter, experiments indicate that a lower limit exists, the value of which depends upon the mt ter design and is independent of the amount of disturbance produced. Thus, where the Reynolds number is below this lower limit, all initial disturbances, no matter how severe, are damped out and the motion consequently falls in the laminar range as the fluid enters the metering turbine. Therefore, the establishment of large initial disturbances in the fluid flowing to the metering turbine to hasten the transition from a laminar flow to a turbulent flow is satisfactory only for fluids of not very high viscosity. Consequently, where high accuracy of fluid measurement is required for fluids of high viscosity, other means for viscosity compensation are employed.

Referring now to FIGURE 5, a further construction embodying the principles of the present invention is illustrated. This embodiment of the invention is adapted for metering viscous fluids and is also identical to that of said now abandoned application Ser. No. 717,863 except for the addition of a viscous drag device 60 to the metering turbine.

With continued reference to FIGURE 5, the viscous drag device 66 comprises a viscous drag drum 62 nonrotatably fixed to a coaxial extension 64 of the meter turbine shaft 65 so that the drum-rotates wtih the turbine shaft. The drum 62 is a hollow, sealed unit with a diameter of such size as to establish a selected close running clearance with the interior wall 6 of the cup 68. Cup 68 is mounted at one end coaxially with the meter turbine 30 within a hollow fluid guide and core section 70 on a flange plate 71 which is secured to the guide mem ber by bolts 72 or other suitable means.

A flat circular end plate 73 is mounted at the upstream open end of the cup 68 to close off the interior thereof from the interior of the guide member 70. Aflixed to the plate 73 by bolts 74 or other suitable means is a hollow receiver cup 75 coaxial with the shaft extension 64.

In order to transport a portion of the fluid which is about to be metered to the receiver cup 75, a small tap-off pipe line 76 of selected diameter is provided and connects at one end to the main fluid transporting pipe line 78 a predetermined distance upstream from the fluid guide member 70.

The other end of the tap-ofi pipe line 76 terminates in the cup 75 so as to communicate with the interior thereof. Thus, a predetermined portion of fluid to be metered which is flowing through the pipe line 78, enters the tap-off pipe line 76 and is conveyed to the interior of the cup 75. This fluid is transferred from the cup 75 through a series of apertures 80 formed in end plate 73 into the recess formed by cup 68 and flows between the interior wall 66 and the drum 62 to radial discharge passageways 82 formed in the flange plate 71. The radially formed discharge passageways 82 open into the annular passageway 84 formed by the meter core section 70 and the tubular meter casing 20 upstream from the turbine meter 30 so as to facilitate the return of the tapped-off fluid to the main body of fluid which is about to be metered.

Consequently, it will be appreciated from the foregoing that the fluid entering the cup 68 which surrounds the drum 62 is always of the same kind and has essentially the same viscosity as the fluid being metered in the main passage 84. The magnitude of the running clearance between the drum 62 and the cup 68 is such that the flow of fluid therebetween is laminar in nature within the meter operating range. Thus, as the drum 62 is rotated a viscous shear force E, is established to resist rotation of the drum. This resisting force R, is of the same nature hereinbefore referred to, the magnitude of which is a function of the amount of surface area of the drum 62. This force F therefore, may be varied as required by axially shortening or lengthening the drum to respectively provide for a lesser or greater drum resisting force.

The viscous resisting force F acting on the drum causes a slip 5,, to be imposed upon the turbine in addition to the slip S, which is established by the fluid resisting force F as the fluid passes through the meter 30. Since the slip 8,, is of the same nature as the slip 8; caused by the fluid viscosity resisting force F the addi tional slip imposed upon the turbine is K S R which when plotted versus the Reynolds number has a curve of the nature of the dotted line of FIGURE 6.

Without the compensatory slip S provided by the viscous drag device 60, the meter of FIGURE 5 is essentially a Type I turbine meter and the meter accuracy curve will take the form of curve 92 that is essentially the same as the accuracy curve of a Type I turbine meter hereinbefore referred to which is not equipped with the viscous drag device 60.

With continued reference to FIGURE 6, when the Type I turbine meter is equipped with the viscous drag device 60 hereinbefore described, the resulting accuracy curve for that meter will be curve 94. By adjusting the length of the drum 62, the resisting force F,,' and consequently the slip S is varied until, at the critical Reynolds number, the slip S is equal to the difference in the slip S; imposed upon the turbine in the turbulent range minus the slip S imposed upon the turbine at the critical Reynolds number. This magnitude of slip S due to the viscous drag on the drum 62 which when added to the natural slip S therefore has the effect of flattening the natural Reynolds number accuracy curve 92. The curve resulting from the addition of the slip S and S is designated at 94 and does not have the hump 96 of the curve 92. Since the Reynolds number accuracy curve 94 is substantially flat above the critical Reynolds number, the meter illustrated in the embodiment of FIGURE 5 will therefore accurately meter fluids at all flow conditions above the critical Reynolds number. The accuracy of a turbine meter having an accuracy curve indicated at 94 is clearly evinced by the fact that the accuracy curve 94 and the ideal value curve (co/Q) designated at 98 of FIGURE 6 are substantially parallel in the Reynolds number ranges above the critical Reynolds number. Consequently, since the slip Sf is constant in ranges above the critical Reynolds number, determination thereof will provide for accurate metering of the fluid.

To further increase the accurate metering range, both the viscous drag device 60 of FIGURE 5 and the turbulence generating device of either FIGURE 1 or FIGURE 2 may be incorporated into a Type I turbine meter so as toprovide for an accurate metering range which is greater than the metering ranges established when either of the devices is used alone.

Referring now to FIGURE 7, another construction embodying the principles of the invention is illustrated and generally comprises a free spinning counter-rotating turbine indicated at (henceforth called free turbine) which is added at -a proper distance in front and upstream from the metering turbine 30 and which is provided with an additional drag device generally designated at 114 in the form of a viscous drag cup as will be described.

With continued reference to FIGURE 7, therefore, the axial flow turbine meter therein shown comprises a cylindrical inlet conduit section 20 having a faired core section 22 supported coaxially therein by spaced struts and an outlet conduit section 26 having a faired core section 28 supported coaxially therein by equiangularly spaced longitudinally extending rib 128. Core section 28 journals the meter turbine 30 and contains a drive train to a register (not shown). Since this structure is identical to the structure shown in said now abandoned application 13 Ser. No. 717,863, no further description thereof will be given with the exceptions hereinafter described.

The exceptions referred to, which result from the fact that the flow direction through the meter of this applica- 1 tion is opposite from that shown in said now abandoned application Ser. No. 717,863, are (1) that the turbine 30 is turned around, that is, as compared with the turbine of said application Ser. No. 717,863, each turbine blade 130 is rotated 180 about the axis of the one of the radiating spokes 132 on which it is mounted, and (2) that the shaft 134 on which the hub 136 of the turbine 30 is mounted is extended sufficiently to provide a clearance between the blades 130 and the adjacent end of core section 28.

To minimize the effect of fluid drag on the metering turbine 30 and thus to increase the metering accuracy thereof, the counter-rotating free turbine 110 is concentrically mounted on shaft 140 independently from metering turbine 30.The shaft 140 is journalled within core section 22 coaxial therewith and with turbine 30 by spaced radial sapphire bearings 142 and 144. Free turbine 110 is resiliently axially restrained against downstream movement by a resiliently backed sapphire thrust bearing carried by support 146.

Free turbine 110 is generally similar in construction to metering turbine 30, having a hub 148 from which radiate equiangularly spaced spokes 150, each supporting a blade 152 at its outer end. The relation between the blade angle of blades 152 is approximately equal and opposite to the blade angle for blades 130 relative to the common rotation axis for turbines 110 and 30' for a purpose as will hereinafter become apparent. The turbines 110 and 30 thus rotate in opposite directions at substantially the same angular velocity.

In order to prevent leakage of fluid around the turbines 110 and 30 so as to facilitate passage of substantially all the fluid through the turbines and thereby improve metering accuracy, annular members 154 and 156 are welded respectively to the adjacent ends of conduit sections 28 and 26. These annular members 154 and 156 are maintained in fixed axially spaced and axially aligned relation by piloting engagement with an annular spacer 158 interposed therebetween and maintained in fluid tight relationship therewith by recessed O-ring type gaskets 160 and 162, and are secured together by connecting equiangularly spaced machine screws 164. Members 154, 156 and 158 define internal annular recesses 166 and 168 proportioned and formed to receive the outer ends of blades 130 and 152 and form turbulent seals about the periphery of the turbine blades 130 and 152 respectively to prevent leakage of fluid to be metered around the turbines 110 and 30 without passing through the blades thereof. Spacer 158 is provided with an integral concentric hub 170 having an outside diameter at its periphery 172 equal to the outside diameter of the cylindrical portions of core sections 28 and 22 and supported coaxially therewith from the outer rim 174 by a plurality of equiangularly spaced radial spokes 176 of which there are preferably three. These spokes 176 are of such size, number and shape that they have no material effect on the fluid flow pattern between turbines 110 and 30.

The spacing between the free turbine 110 and meter turbine 30 is important in determining the overall performance of the turbine meter and is short enough so that the tangential component of the fluid exit velocity from the free turbine is not significantly reduced by the fluid friction-when passing through the spacing. Howevegit is long enough so that the effect of the disturbance created upstream by the presence of the counter-rotating free turbine is small when it reaches the meter turbine. Experimental results indicate that this spacing should be at least equal to the chord length of the free turbine blades.

To apply a supplemental drag to free turbine 110, a cylindrical drum 178 is fixed to the end of shaft 140 opposite the end on which the turbine 110 is fixed. A cup 180, having a cylindrical recess 182 formed therein of such size to freely receive drum 178 therein, is provided with an integral coaxial shaft 184 guided by bearings 186 and 188 for axial sliding movement coaxial with shaft 148. Bearings 186 and 188 are suitably and conventionally mounted in the core section 22 as shown. The cup 180 may be shifted axially to the left as viewed in FIGURE 7 to surround a selected portion of the drum 178 by rotary manipulation of a shaft 190 which has a gear 192 fixed thereto and in constant mesh with a rack 194 formed on shaft 184.

The cavity 196 formed by core section 22, in which cup 180 and drum 178 are disposed, is in fluid communication with the annular channel 197 through which the fluidto be metered flows via the openings 198 on the end plate 200 of core section 22 so that cavity 196 becomes filled with fluid of the same viscosity as that being metered. The outside diameter of the drum 178 is sufliciently smaller than the diameter of recess 182 so that there is a slight radial clearance space between the outside of the drum 178 and the cylindrical wall of recess 182.

As the radial clearance space between the drum 178 and the cup 180 is filled with liquid, a supplemental drag is applied to the turbine 110, which drag is a function of the viscosity of the fluid, the radial depth of the clearance space and the surface of overlap of cup 180 relative to the drum 178. Although the amount of overlap is shown and described to be adjustable in connection with this embodiment, most installations are provided with an ad justment that is factory-set.

By this construction of the addition of the free-spinning turbine rotor in front of the meter turbine 30 wherein the turbine 110 is free of any load other than the fluid friction acting upon it and the effects of the viscous drag drum and the fluid load of the turbine shaft bearings which is negligible, the tangential component of the absolute fluid exit velocity from the free turbine 110 will be a function of the viscosity of the fluid about to be metered. This tangential velocity component will, as the fluid to be metered enters the meter turbine 30, apply a supplemental driving force to the meter turbine. This supplemental driving force may be theoretically equal and opposite to the total resisting force acting on the meter turbine so that the absolute fluid exit angle and tangential component of the absolute exit velocity of the fluid from the blades of the metering turbine are zero under ideal conditions. In practice, however, this ideal condition is not fully achieved but rather by the provision of the free counter rotating turbine 110 with the controlled viscous drag device 114, the discrepancy of registration attributable to the viscosity effect of the fluid is reduced to a point where it is negligibly small as will hereinafter become apparent.

Analysis shows that the accuracy of the turbine meter 30 is affected only by the difference of the resisting forces due to fluid friction acting on the meter turbine 30 and on the free turbine 110 and which are respectively designated as P and F The accuracy of the turbine meter alone without the free turbine is affected by the absolute magnitude of the resisting force F due to fluid friction acting on the meter turbine. This resisting force F is substantially large and is of such magnitude as to result in substantial inaccuracies in metering fluids of high viscosity. However, the difference between the resisting forces due to fluid drag (F minus F is by the present embodiment made sufliciently small for all flows within its operating range by controlling the viscous drag device 114 so that the resisting force F is equal to the resisting force F The equivalency of the fluid resisting forces can be accomplished by controlling the parameters which determine the amount of fluid friction acting on the free turbine; When such equivalency and magnitude is facilitated (i.e., F F the accuracy of the turbine meter 30 becomes substantially independent of the viscosity of the fluid.

Referring to FIGURE 8, the effect of the free turbine 15 110 on the meter turbine 30' at synchronous condition is diagrammatically illustrated by velocity diagrams in relation to the blades 130 and 152 of the turbine. The velocity v is the velocity of the fluid entering the free turbine and is assumed to be totally axial and uniformly distributed as hereinbefore described in the analysis of the type I turbine meter. The fluid thus entering the free turbine 110 with velocity v causes it to turn with an angular velocity w so that the blades 152 move with a corresponding linear velocity of rw. Since the free turbine 110 has a resisting force F imposed upon it as a result of the fluid friction the fluid entering with the initial velocity v; undergoes a change in magnitude and direction as it passes through the free turbine so that it assumes an exit velocity designated at v Similar to the analysis of the type I turbine meter, this exit velocity v exiting from the free turbine 110 has a tangential velocity component w which directly evinces this slip of the free turbine due to its resisting forces. This exit velocity v corresponds esrsentially to the inlet velocity 11 to the metering turbine 30 and which is no longer totally axial but rather is provided with the tangential component v corresponding to the exit tangential component v The component velocity V is equal in magnitude and direction to the tangential component v of the free turbine outlet velocity.

Since the free turbine 110 is structurally similar to the metering turbine 30 but having its blades slanted in a direction that is opposite to that of the metering turbine, the metering turbine 30 therefore rotates with an angular velocity m which is opposite in direction to the angular velocity w' of the free turbine.

With continued reference to FIGURE 8, the fluid leaves the metering turbine 30 with an absolute velocity 11., which will be very close to being purely axial in direction. In the ideal condition, velocity 11.; will be purely axial; however, it may have some very small tangential component v It will be apparent from the foregoing that the change in tangential velocity Av, required to drive the metering turbine is, in accordance with the present embodiment of the invention, no longer reflected by a tangential component of the meter turbine outlet velocity v but rather, constitutes the change in tangential velocity from the non- :axial velocity v to the purely axial velocity v Thus, where the tangential component v of the inlet velocity to the :metering rotor is of the proper magnitude, it provides the driving force F required to overcome the resisting forces F due to fluid friction on the metering turbine 30 :and the exit velocity v, from the metering turbine will :always be purely axial. Further, where the tangential component v of the inlet velocity to the metering turbine 30 is made to vary in accordance with the fluid resisting forces F on the metering turbine 30, the metering turbine will Produce a constant ratio of turbine speed to flow rate w/ Q.

In order to make the tangential component v of the free turbine outlet velocity of suflicient magnitude to overcome the metering turbine fluid resisting forces, the viscosity drag device 114 is utilized. The main reason for this is as follows: For fluids of very high viscosity, the Reynolds number is very low. At very low Reynolds number, the free turbine 110 has more slip than the meter turbine 30 since the latter has the help of the former. As the fluid friction is essentially proportional to the turbine speed, the fluid friction F on the meter turbine will be greater than that F on the free turbine if the two turbines are similar and have the same amount of viscous drag surface. This difference in the fluid frictions (F -F can be greatly reduced by providing the free turbine 110 with a proper amount of additional viscous drag surface which is in excess of the viscous drag surface on the meter turbine and this is accomplished by providing an additional viscous drag surface in the form of the viscous drag drum 178 shown in FIGURE 7 and hereinbefore described. The desirable amount of additional viscous drag surface provided for by utilization of the drag drum I6 17 8 is obtained by adjusting the axial position of the nonrotating cup 189 with respect to the rotating drum 17 8 of the free turbine 110. Consequently, the free turbine of FIGURE 7 compensates for the viscosity effect below the critical Reynolds number (laminar flow range) as Well as above the critical Reynolds number.

The invention may be embodied in other specific forms without departing from the spirit or essential characteris tics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

What is claimed and desired to be secured by United States Letters Patent is:

1. In an axial flow impulse turbine for use in accurately measuring the flow of viscous fluids, a housing, means defining an annular fluid passageway through said housing, a metering turbine having a plurality of blades movable in a concentric path within said passageway in response to the flow of fluid, and means for applying a supplemental compensating torque to said turbine to overcome the resisting torque due to the fluid friction exerted on the said metering turbine comprising a free spinning counterrotating turbine independently mounted at a predetermined distance upstream from said metering turbine and having a plurality of blades movable in response to the flow of fluid in a concentric path within said passageway in axial alignment with the path of said metering turbine blades, the blade angle of the blading of said counterrotating turbine being substantially equal and oppositely inclined relative to the blading angle of said metering turbine for imparting a tangential fluid velocity component substantially opposite to the change of tangential velocity component of fluid passing through the metering turbine, and means for applying an additional viscous drag of predetermined magnitude to said counterrotating turbine for establishing a tangential fluid velocity component equal in magnitude to the change of tangential fluid velocity component of said metering turbine.

2. In an axial flow impulse type turbine meter for accurately measuring the flow of viscous fluids, a housing, means defining an annular fluid flow passageway through said housing, a metering element rotatably mounted in said housing for rotation in response to the flow of fluid through said passageway, a turbine rotor rotatably mounted in said housing independently from said metering element and in axial alignment with the rotational axis of said metering element at a predetermined distance upstream from said metering element, said turbine rotor being rotatable in response to the flow of fluid through said annular passageway for applying a supplemental driving torque to said metering element, and means for controlling the magnitude of said supplemental driving torque whereby the supplemental driving torque applied to said metering element is substantially equal to the resisting torque due to fluid friction exerted on said metering element, said torque controlling means comprising a drum mounted for rotation with said turbine rotor in the fluid being metered, a cup mounted concentrically withv said drum to define a slight annular clearance space between the outer surface of said drum and said cup, and means for axially moving said cup to vary the surface of said drum overlapped by said cup.

3. A turbine meter comprising'a housing having fluid inlet and outlet openings, a bladed metering rotor mounted in said housing for rotation by fluid flow therethrough and adapted to drive a registering mechanism, and viscosity compensating means comprising a bladed counterrotating rotor independently mounted in said housing at a predetermined distance upstream from said metering rotor and-being rotated in a direction opposite to said metering rotor by fluid flow through said housing to apply a supplemental drive torque to said metering rotor and means for controlling said supplemental drive torque by applying a drag to said counter-rotating rotor, said drag applying means being responsive to the viscosity of the fluid flowing through said housing to vary said drag in accordance with the viscosity variations of the fluid being metered.

4. The turbine meter defined in claim 3 wherein the blades of said counterrotating rotor are oppositely inclined with respect to the blades of said metering rotor to impart a predetermined velocity component to the motive fluid flowing into the metering rotor, said velocity component providing said supplemental drive torque.

5. The turbine meter defined in claim 3 comprising means for selectively adjusting the magnitude of the drag applied to said counterrotating rotor by said viscosity compensating means.

6. The turbine meter defined in claim 4 wherein said viscosity compensating means comprises a pair of elements having overlapping, spaced apart surfaces, means coupling one of said elements to said counterrotating rotor for rotation therewith relative to the other of said elements, and means for transporting at least a portion of the fluid being metered between the overlapping surfaces of said elements, said elements being arranged sufficiently close to each other that relative rotation of said elements produces said drag.

7. The turbine meter defined in claim 6 comprising means for selectively adjusting the extent by which said surfaces overlap each other to vary the magnitude of said drag.

8. The turbine meter defined in claim 4 wherein said viscosity compensating means comprises a pair of elements having opposed, concentric, spaced apart surfaces of revolution, means coupling one of said elements to said counterrotating rotor for rotation therewith relative to the other of said elements, means for transporting at least a portion of the fluid being metered between said overlapping surfaces, said surfaces of revolution being arranged sufficiently close to each other that relative rotation of said elements produces said drag, and means for selectively adjusting the axial position of one of said elements relative to the other of said elements to vary the magnitude of said drag by varying the area by which one of the surfaces of revolution overlaps the other of said surfaces of revolution.

9. The turbine meter defined in claim 8 wherein the one of said elements that is coupled to said counterrotating rotor comprises a drum and wherein the other of said elements comprises a hollow part adapted to coaxially receive said drum, said drum and said part being axially aligned with said counterrotating rotor.

10. The turbine meter defined in claim 9 wherein the axially adjustable one of said elements is said part.

11. The turbine meter defined in claim 9 comprising a fluid guide core structure rotatably supporting said mew tering and counterrotating rotors and being mounted in said housing for directing motive fluid through the blades of said metering and counterrotating rotors in a stream of annular cross section, said drum and said part being mounted in a portion of said fluid guide core structure.

12. The turbine meter defined in claim 4 comprising a fluid guide core structure rotatably supporting said metering and counterrotating rotors in axial alignment with each other, said fluid guide core structure being mounted in said housing for directing motive fluid through the blades of said metering and counterrotating rotors in a stream of annular cross section extending in coaxial relation to the rotational axes of said rotors.

13. The turbine meter defined in claim 12 comprising means for selectively adjusting the magnitude of the drag applied to said counterrotating rotor by said viscosity compensating means.

References Cited UNITED STATES PATENTS 1,020,127 3/1912 Coleman 73--230 1,963,904 6/1934 Hodgson 7323O 3,053,086 9/1962 Granberg 73-230 3,135,116 6/1964 Kwong et a1 73231 3,241,366 3/1966 Allen 73-230 FOREIGN PATENTS 14,060 4/1852 Great Britain.

RICHARD C. QUIESSER, Primary Examiner. JAMES J. GILL, Examiner.

EDWARD D. GILHOOLY, Assistant Examiner. 

3. A TURBINE METER COMPRISING A HOUSING HAVING FLUID INLET AND OUTLET OPENINGS, A BLADED METERING ROTOR MOUNTED IN SAID HOUSING FOR ROTATION BY FLUID FLOW THERETHROUGH AND ADAPTED TO DRIVE A REGISTERING MECHANISM, AND VISCOSITY COMPENSATING MEANS COMPRISING A BLADED COUNTERROTATING ROTOR INDEPENDENTLY MOUNTED IN SAID HOUSING AT A PREDETERMINED DISTANCE UPSTREAM FROM SAID METERING ROTOR AND BEING ROTATED IN A DIRECTION OPPOSITE TO SAID METERING ROTOR BY FLUID FLOW THROUGH SAID HOUSING TO APPLY A SUPPLEMENTAL DRIVE TORQUE TO SAID METERING ROTOR AND MEANS FOR CONTROLLING SAID SUPPLEMENTAL DRIVE TORQUE BY APPLYING A DRAG TO SAID COUNTER-ROTATING ROTOR, SAID DRAG APPLYING MEANS BEING RESPONSIVE TO THE VISCOSITY OF THE FLUID FLOWING THROUGH SAID HOUSING TO VARY SAID DRAG IN ACCORDANCE WITH THE VISCOSITY VARIATIONS OF THE FLUID BEING METERED. 